Wireless communication apparatus and method for compensating offset using the same

ABSTRACT

A wireless communication system, apparatus and a method for compensating offset using the same are disclosed, in which offset due to latency in a power save mode is compensated. The wireless communication apparatus includes a frequency matched unit for compensating offset due to latency that may occur during communication between the wireless communication apparatus and external equipment. The frequency matched unit adds a predetermined time to a clock value of a system clock if power save mode is transited to normal mode. Thus, the offset generated can efficiently be compensated if the power save mode is transited to the normal mode.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation of application Ser. No. 10/247,814filed on Sep. 20, 2002 for WIRELESS COMMUNICATION APPARATUS AND METHODFOR COMPENSATING OFFSET USING THE SAME, which is incorporated byreference in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication apparatus anda method for compensating offset using the same, and more particularly,to a wireless communication apparatus and a method for compensatingoffset using the same in which latency generated in a power save modecan efficiently be compensated.

2. Description of the Related Art

Bluetooth is a name for a wireless data communication technology in thefield of electrical communication, networking, computing, and consumergoods. The Bluetooth technology serves to connect various apparatusesthrough one wireless connection operating over a short distance. Forexample, if the Bluetooth wireless communication technology isimplemented in cellular phones and laptop computers, the cellular phonesand laptop computers can communicate among themselves without cables.All digital equipment as well as printers, personal digital assistants(PDA), desk top computers, facsimiles, keyboards, and joy sticks may bea part of the Bluetooth system.

Generally, the Bluetooth system has a maximum data transmission of 1Mbps and a maximum transmission distance of 10 m. 1 Mbps is a frequencywithin an industrial scientific medical (ISM) frequency band of 2.4 GHzthat can be used without any permission, and can readily be realized ata low cost. Also, the transmission distance of 10 m has been establishedbecause it is a sufficient transmission distance between a user'sportable equipment and a personal computer on a desk in an office.

Furthermore, since the Bluetooth system has been devised to operate inthe radio frequency environment where a lot of noise exists, a frequencyhopping system of 1600 times per second is used to provide stable datatransmission and reception in such a radio frequency environment havinga lot of noise.

Moreover, the Bluetooth system supports one-to-multiple connection aswell as one-to-one connection. As shown in FIG. 1, in the Bluetoothsystem, a plurality of piconets can be constructed and connected,respective piconets being divided by different frequency hopping orders.The term “piconet” means a Bluetooth unit formed by connecting one ormore slaves to one master device. A piconet can have one master and amaximum of seven slaves. The master equipment and the slave equipmentimplement bi-directional communication by means of time division duplex(TDD) based on 1 hopping slot of 625 μs (1/1600 second). The pluralityof piconets systematically connected with one another constitute ascatternet.

FIG. 2 illustrates communication between the master and the slaves bymeans of the TDD. Referring to FIG. 2, each channel allocated to timeslots has a length of 625 μs. The number of time slots is determined bya Bluetooth clock of the piconet master. Also, the master and the slavecan alternatively transmit packets. That is, the master transmitspackets in only the time slot marked by an even number. The slavetransmits packets in only the time slot marked by an odd number. Thepackets transmitted by the master or the slave should be provided withinfive time slots. A packet is a unit of data transmitted on a piconetchannel.

The piconet is synchronized with the system clock of the master. Thesystem clock of the master is never corrected as long as the piconetexists. The system clock of the master is maintained in a period ofM×625 μs during successive transmissions, where M is an even number anda positive integer.

The slave updates timing offset to match with the master clock. That isto say, the slave compares a test RX timing with an exact RX timing of areceived packet so as to update offset for compensating a timing error.

The slave TX timing should be based on the latest slave RX timing. TheRX timing is based on the last successive trigger during a slot from themaster to the slave. The slave can receive a packet and can correct theRX timing as long as timing inconsistency remains in a window ofuncertainty of ±10 μs.

When the Bluetooth system is connected, the master can manage the slavein a hold mode, a sniff mode, a park mode, and so on, in order to savepower. The hold mode retains an active member address AM_ADDR in a statewhere the master is connected with the slave, and proceeds into a sleepstate. The sniff mode retains an active member address AM_ADDR in astate where the master is connected with the slave, and extends a listeninterval. The park mode proceeds into a sleep state by opening an activemember address AM_ADDR in a state where the master is connected with theslave. Before the slave proceeds into the park mode, a park mode addressPM_ADDR or an access request address AR_ADDR is assigned from themaster.

FIG. 3 illustrates an RX/TX cycle of a Bluetooth master in a normal modefor a single slot packet, and FIG. 4 illustrates an RX/TX cycle of aBluetooth slave in a normal mode for a single slot packet. As shown inFIGS. 3 and 4, the Bluetooth system selectively transmits and receives apacket in a state where the master is connected with the slave. Themaximum size of the packet may be 366 μs depending on the type of packetand the load length. The RX transmission and the TX transmission havedifferent hopping frequencies. The channel hopping frequency is denotedby g(m).

Once the transmission is implemented, the return packet is estimated asN×625 μs after a TX burst starts, wherein N is an odd number and apositive integer. Also, N depends on the type of the transmitted packet.The window has a length of 20 μs during normal operation, which assureslatency of +/−10 μs.

If the master of the Bluetooth system is transited to an active state ina state where it manages the slave in a hold mode, a sniff mode, or apark mode, offset may occur between the master and the slave. That is,latency of +/31 10 μs is assured while the Bluetooth system isconnected. If such latency is accumulated in a power save mode for along time (>40 sec.), the Bluetooth system, which employs a frequencyhopping spread spectrum (FHSS), fails to transmit data even under theconnection state. Referring to FIG. 5, the Bluetooth system may be in ahold mode under the connection state. In the hold mode, the Bluetoothsystem neither transmits nor receives data. If the slave of theBluetooth system is returned to a normal mode, the slave should check,before transmitting data to the master, whether there has been anyrequest signal from the master. In this case, the size of a searchwindow of the slave can increase from +/−10 μs to Xμs as shown.

If the size of the search window exceeds 625 μs, the following windowstarts not at the RX hopping frequency g(2m), g(2m+2), . . . , g(2m+2i)(where, i is an integer) but at g(2m), g(2m+4), . . . , g(2m+4i).Alternatively, the following window starts at g(2m), g(2m+6), . . . ,g(2m+6i). In this case, a problem arises in that inconsistency of thehopping frequency is caused, thereby exceeding a limited time of 40 sec.

To prevent such a problem from occurring, an experimental estimatedvalue, derived from many experiments, should be provided. In this case,however, power conservation features may be lost. Also, if a hold modeof 40.9 sec. is used, the maximum latency of 32.750 ms should becompensated, thereby exceeding 625 μs.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea wireless communication apparatus and a method for compensating offsetusing the same in which a window size of a microsecond unit is enlargedin a frame unit to more efficiently compensate latency.

In order to achieve the above-described objects of the presentinvention, there is provided a wireless communication apparatus whichincludes a transceiver for transmitting and receiving data packets toand from an external equipment; and a frequency matched unit forcompensating an offset due to latency that may occur duringcommunication between the wireless communication apparatus and theexternal equipment by adding a clock value corresponding topredetermined frames to a clock value of a system clock if any one of ahold mode, a sniff mode, or a park mode is transited to a normal mode.

The frequency matched unit includes a hopping frequency calculator forcalculating a hopping frequency of the frames from the added value; anaccess code searcher for searching an access code provided in the datapackets; a counter for counting the number of the frames; and acontroller for compensating a frequency of the frames to the hoppingfrequency so that the offset is compensated. The controller controls thehopping frequency calculator, the access code searcher, and the counter,so that the offset is compensated if the access code is searched. Thecontroller also determines whether the frames have been ended if theaccess code is not searched, counts the frames if it is determined thatthe frames have not been ended, and controls the counter and the accesscode searcher to search the access code. Also, the controller obtainsthe clock value corresponding to the frames from the number of theframes counted by the counter, one frame in the frames having a lengthof 1.25 ms which is one frame length in an FHSS system.

In the wireless communication apparatus according to the presentinvention, since a window size of a microsecond unit is enlarged in aframe unit, latency can be compensated more efficiently.

There is also provided a wireless communicating method including thesteps of transmitting and receiving data packets to and from an externalequipment; and compensating offset due to latency that may occur duringcommunication between a wireless communication apparatus and theexternal equipment by adding a clock value corresponding topredetermined frames to a clock value of a system clock if any one of ahold mode, a sniff mode, or a park mode is transited to a normal mode.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 illustrates a scatternet of a Bluetooth system;

FIG. 2 illustrates communication between a master and a slave by meansof a TDD;

FIG. 3 illustrates an RX/TX cycle of a Bluetooth master in a normal modefor a single slot packet;

FIG. 4 illustrates an RX/TX cycle of a Bluetooth slave in a normal modefor a single slot packet;

FIG. 5 illustrates an RX timing of a slave if it is returned from a holdstate;

FIG. 6 is a block diagram illustrating a wireless communicationapparatus according to the present invention;

FIG. 7 illustrates a Bluetooth clock;

FIG. 8 illustrates a window size enlarged in a frame unit of FIG. 6;

FIG. 9 illustrates an example of offset compensated between a master anda slave of FIG. 8; and

FIG. 10 is a flow chart illustrating a method for compensating offset inthe wireless communication apparatus of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A wireless communication apparatus and a method for compensating offsetusing the same in accordance with preferred embodiments of the presentinvention will now be described in detail with reference to theaccompanying drawings.

FIG. 6 is a block diagram illustrating a wireless communicationapparatus according to the present invention.

Referring to FIG. 6, a wireless communication apparatus 20(30) accordingto the present invention includes a transceiver 21(31) and a frequencymatched unit 23(33). The frequency matched unit 23(33) includes ahopping frequency calculator 25(35), an access code searcher 26(36), acontroller 27(37), and a counter 28(38). There is provided a host 40(50)as a peripheral element of the wireless communication apparatus 20(30).The reference numerals 20, 21, 23, 25, 26, 27, 28, and 40 represent thewireless communication apparatus and its elements operated as a slavewhile the reference numerals 30, 31, 33, 35, 36, 37, 38, and 50represent the wireless communication apparatus and its elements operatedas a master.

First, the wireless communication apparatus 20 operated as a slave willbe described.

The transceiver 21 processes an externally received signal, such as aradio frequency (RF) signal and externally transmits data packets to betransmitted.

The frequency matched unit 23 is connected to the host 40 through acommunication interface. Various communication terminals such asnotebook computers, cellular phones, and printers may be used as thehost 40. The frequency matched unit 23 processes a signal requested bythe host 40 and also processes a signal received through the transceiver21. Furthermore, if any one of a hold mode, a sniff mode, and a parkmode is transited to a normal mode, the frequency matched unit 23 adds aclock value corresponding to predetermined frames to a clock value of asystem clock (not shown) provided in the wireless communicationapparatus 20 so that offset due to latency that may occur duringcommunication between the wireless communication apparatus and anexternal equipment is compensated.

The hopping frequency calculator 25 calculates a frame hopping frequencyfrom a value obtained by adding a clock value corresponding to theframes to the clock value of the system clock in the wirelesscommunication apparatus 20.

The access code searcher 26 searches an access code provided in a datapacket. The access code is provided in a data packet transmitted from apiconet channel. The data packet starts with the access code. The accesscode is used for signal synchronization as well as DC offsetcompensation and signal identification.

The controller 27 controls the hopping frequency calculator 25, theaccess code searcher 26, and the counter 28 so that the frame frequencyis compensated by the obtained hopping frequency to compensate offset.

The counter 28 counts the number of frames. The number of frames countedby the counter 28 is transmitted to the controller 27. Based on thenumber of frames received from the counter 28, the controller 27 obtainsa clock value corresponding to the frames.

Next, the wireless communication apparatus 30 operated as a master willbe described.

When the wireless communication apparatus 30 is operated as a master, itmay request any one of the slaves to function as a master for apredetermined time. The master determines the overall characteristics ofa channel within a piconet. A bluetooth device address BD_ADDR of themaster determines a frequency hopping row and a channel access code.That is, a clock of the master determines a phase of a hopping row and atiming. Also, the master controls the traffic on a channel. Any of thedigital equipment may be used as the master. If a piconet is formed,functions of the master may be reversed to those of the slave.

The frequency matched unit 33 exchanges a data transmission timing withthe slaves connected to a network, and transmits and processes piconetdata including an active member address of the slaves connected to thenetwork.

FIG. 7 illustrates clocks of a Bluetooth system. The Bluetooth systemincludes an internal system clock (hereinafter, referred to as aBluetooth clock) that determines hopping and timing of transmission andreception. The Bluetooth clock is neither changed nor controlled.However, mutually synchronized temporary Bluetooth clocks obtained byadding an offset value to the original clock may be provided tosynchronize with the other equipment.

The timing and the frequency hopping of the channel on the piconet aredetermined by the Bluetooth clock of the master. When the piconet isestablished, the clock of the master communicates with the slaves. Eachslave adds an offset value to each slave clock to synchronize with theclock of the master. Since clocks of respective equipment may bedifferently driven, respective offset values should periodically beupdated.

In the Bluetooth system, four periods, 312.5 μs, 625 μs, 1.25 ms, and1.28 s correspond to timer bits, CLK0, CLK1, CLK2, and CLK12.Transmission from the master to the slaves starts in an even numberedperiod when CLK0 and CLK1 are all 0.

FIG. 8 illustrates a window size enlarged in a frame unit of FIG. 6, andFIG. 9 illustrates an example of offset compensated between the masterand the slave of FIG. 8.

Referring to FIGS. 8 and 9, predetermined frames are obtained bycalculating Hop 2 m based on the hold mode or the sniff mode. Thetransceiver 21(31) of the wireless communication apparatus 20(30)transmits and receives data packets to and from the external equipment.The data packets refer to a unit of data transmitted through the piconetchannel. Each data packet includes three elements, an access code, aheader, and a payload. The access code and the header have a fixed size,generally 72 bits and 54 bits. The payload may have a size between 0 and2745 bits. There are various types of packet, such as an access codetype packet, an access code and header type packet, an access code andpayload type packet, and so on.

The packet starts with the access code. If the header follows after theaccess code, the access code has a length of 72 bits. If no headerfollows, the access code has a length of 68 bits. The access code isused for signal synchronization, DC offset compensation, and signalidentification. The access code can identify all the packets transmittedand received on the piconet channel.

The frequency matched unit 23(33) compensates latency for the clockvalue of the frames to be transmitted and received, if the wirelesscommunication apparatus 20(30) is transited from any one of the holdmode, the sniff mode, and the park mode to a normal mode, i.e., anaccess mode. A method for compensating offset of the latency will bedescribed with reference to FIG. 10.

FIG. 10 is a flow chart illustrating a method for compensating offset inthe wireless communication apparatus of FIG. 6.

Referring to FIG. 10, the transceiver 21(31) of the wirelesscommunication apparatus 20(30) transmits and receives data packets toand from the external equipment. The frequency matched unit 23(33) ofthe wireless communication apparatus 20(30) determines whether thewireless communication apparatus 20(30) has been transited from any oneof the hold mode, the sniff mode, and the park mode to the normal mode(S101). If the wireless communication apparatus 20(30) has beentransited from any one of the hold mode, the sniff mode, and the parkmode to the normal mode, the frequency matched unit 23(33) enables asearch window for the frames to be transmitted and received (S103). Thecounter 28(38) of the frequency matched unit 23(33) counts the number ofthe frames to be transmitted and received. The number of the frames tobe transmitted and received refers to a frame unit conversion factor ofthe data packets in a standby state without being transmitted to theexternal equipment during the hold mode, the sniff mode, or the parkmode. The frequency matched unit 23(33) obtains a clock valuecorresponding to the counted frames. Also, the frequency matched unit23(33) adds the clock value of the obtained frames to the clock value ofthe wireless communication apparatus 20(30), i.e., the Bluetooth clockvalue. The frequency matched unit 23(33) obtains the hopping frequencyfor the frames to be transmitted and received, from an inverse numbervalue of the value obtained by adding the clock value of the frames tobe transmitted and received to the Bluetooth clock value (S105). Thefrequency matched unit 23(33) hops the frames to be transmitted andreceived with the calculated hopping frequency. One frame in the framesto be transmitted and received has a length of 1.25 ms which is oneframe length in the FHSS system. The FHSS system is one of tworepresentative spread band technologies, and the other is a directsequence spread spectrum (DSSS) system. The DSSS system modulates theoriginal signal with a greater bandwidth than a data bandwidth andspreads the modulated signal. While the FHSS system moves data from onefrequency to another frequency by means of a programmed order or randomsequence, and its receiving party should identify movement of thefrequency. The FHSS system has an advantage in that it is lesssusceptible to an interference phenomenon than the DSSS system.

Furthermore, the frequency matched unit 23(33) determines whether theaccess code has been searched from the frames to be transmitted andreceived (S107). Once the access code has been searched from the framesto be transmitted and received, the frequency matched unit 23(33)disables the search window (S109), and is connected to the slave or amaster of another piconet to transmit and receive data packets (S111).

If the access code has not been searched from the frames to betransmitted and received, the frequency matched unit 23(33) determineswhether the frames to be transmitted and received have been ended(S113).

If it is determined that the frames to be transmitted and received havebeen ended, the frequency matched unit 23(33) determines that the framesdo not communicate with the external equipment and that connection ofthe slave has failed (S117).

If it is determined that the frames to be transmitted and received havenot been ended, the frequency matched unit 23(33) counts the frames tobe transmitted and received, so that the above method is repeatedlyimplemented for the next frame. Thus, offset generated in the frames tobe transmitted and received can efficiently be compensated if thewireless communication apparatus is transited from the hold mode, thesniff mode, or the park mode to the normal mode. In the wirelesscommunication apparatus according to the present invention, since thewindow size of a microsecond unit is enlarged in a frame unit, thelatency can be compensated more efficiently.

1. A wireless communication system comprising: external equipment; andan apparatus comprising: a transceiver for transmitting and receivingdata packets to and from the external equipment; and a frequency matchedunit for compensating an offset due to latency that may occur duringcommunication between the apparatus and the external equipment by addinga predetermined time to a clock value of a system clock if power savemode is transited to normal mode.
 2. The wireless communication systemof claim 1, wherein the external equipment further comprises at leastone additional apparatus, and wherein at least one of said apparatusesis a master apparatus and at least one of said apparatuses is a slaveapparatus.
 3. The wireless communication system of claim 2, wherein eachmaster apparatus controls each said slave apparatus associated with themaster.
 4. The wireless communication system of claim 3, wherein thefrequency matching unit of each said associated slave apparatus adds anoffset value to each slave clock so as to synchronize said slave clockwith the clock of the master apparatus.
 5. The wireless communicationsystem of claim 3, wherein the master apparatus manages each saidassociated slave apparatus in the normal mode and in the power savemode.
 6. The wireless communication system of claim 4, wherein the powersave mode is a hold mode, a sniff mode or a park mode.
 7. The wirelesscommunication system of claim 2, wherein the master apparatus is acommunication terminal.
 8. The wireless communication system of claim 6,wherein the communication terminal is a computer, a cellular phone or aprinter.
 9. A wireless communication apparatus comprising: a transceiverfor transmitting and receiving data packets to and from externalequipment; and a frequency matched unit for compensating an offset dueto latency that may occur during communication between the apparatus andthe external equipment by adding a predetermined time to a clock valueof a system clock if power save mode is transited to normal mode. 10.The wireless communication apparatus of claim 9, wherein the power savemode is a hold mode, a sniff mode or a park mode.
 11. The wirelesscommunication apparatus of claim 9, wherein the apparatus is digitalequipment.
 12. The wireless communication apparatus of claim 9, whereinthe apparatus is a cellular phone, a laptop computer, a printer, apersonal digital assistant(PDA), a desk top computer, a facsimile, akeyboard, or a joy stick.
 13. A wireless communication methodcomprising: transmitting and receiving data packets to and from externalequipment; and compensating offset due to latency that may occur duringcommunication between an apparatus and the external equipment by addinga predetermined time to a clock value of a system clock if power savemode is transited to normal mode.
 14. The wireless communication methodof claim 13, wherein the power save mode is a hold mode, a sniff mode ora park mode.
 15. A method of operating a wireless communication system,comprising: selecting an apparatus to serve as a master apparatus,wherein any additionally connected apparatus is a slave apparatus, andall connected apparatuses make up a piconet; calculating a frequencyhopping row and a channel access code of a channel within the piconetbased on a system clock of the master apparatus; wherein each said slaveapparatus adds an offset value to each slave clock to synchronize theslave clock with the system clock of the master apparatus; andtransmitting and receiving data packets to and from the apparatuses inthe piconet.